Most Harry Potter fans know that there's a big twist in the final chapter of Harry Potter and the Deathly Hallows. But no one really knew how the crew will film this, until actor Tom Felton explained. Spoilers ahead.

For those of you who haven't read it yet, in the final book there's a flash-forward scene, and we see our heroes in their late 30s. Needless to say, everyone is worried the director might merely hire all new actors for the roles. Last year, the director assured us that hiring new cast members was not an option. And that the crew was currently pondering using all sorts of technology to age the faces of our three favorite Hogwarts students:

Harry Potter lovers know that in the final chapter of Harry Potter and the Deathly Hallows, there…
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David Yates: Probably not Benjamin Button technology. We did look into that. But we don't think it's the route we're going to take.

David Heyman: Benjamin Button technology was used to make him look younger, but we're taking people who are 20 years old, and making them look like they're in their late 30s. So that's a different experience. And we may use some of the techniques from Benjamin Button technology, but we're still exploring. We're going to do everything we can - but it will be Dan, Rupert and Emma, not someone else.

But it seems like they finally figured it out, by bringing in a different kind of acting coach, who's teaching the now 20-something students how to age themselves about twenty years. Tom Felton, who plays Draco Malfoy, explained to MTV:

"For nearly two months, we've all been doing prosthetic tests and all sorts of preparation for the epilogue," Felton said. "I've been having some aging training. You've got to walk differently. There's a slump in your walk.... It's bizarre," Felton laughed. "We have a lovely guy who comes in. It was a little weird the first time - imagine you've got weights on your arms! There have been a number of times where I nearly laughed and I had to hold it in."